Antenna counterpoise system



Feb. 13, 1934. H T. FRHS ANTENNA COUNTERPOI SE SYSTEM Filed Jan. 11, 1930 ATTORNEY Patented Feb. 13,, 1934 1.947.256 ANTENNA COUNTERPOISE SYSTEM Harald T. Friis, Rumson, N. J., assig'nor to Bell Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application January 11', 1930. Serial No. 420,082

9 Claims.

This invention relates to antenna systems and more particularly to counterpoise arrangements associated with antenna systems.

antenna systems. haps have not proved as effective as the grounded arrangements,

While in general they peror satisfactory and many of 1 them at present in use are employed more as a matter of necessity rather than of preference,

in certain systems including systems wherein a good ground is available, they are especially effective as compared with the grounded arrangei ments. For example, in directional systems employing a plurality of antenna units a counterpoise may be easily arranged to ment of the impedances between individual units so that the phase permit adjustitself and the of the currents ;in the various units may be rendered similar.

One of the inherent disadvant cally all counterpoises as at prese ages of practint employed, is

that it absorbs energy which opposes that induced in the antenna proper.

It is an object of this invention to improve the operation of transmitting and receiving antennae.

It is another object of this invention to elimi-,

nate the effects of voltages induce poise.

It is still another ob minimize the impedance of the an poise system.

d in a counter ject of this invention to tenna-counter- It is an additional object of this invention to improve the directional characteristicsof directive systems employing a plurality of antenna elements.

One feature of the invention resides in the use of two quarter wave length open-ended conductors conductively and coline form a double counterpoise. Th

arly joined to is counterpoise direction.

Another feature of the inventio 11 comprises an adjustable impedance inserted in a common down lead to the counterpoise or ground from two or more antennae for the primary purpose of securing a desired phase difference between the respective antenna currents.

In one embodiment of the invention a counterpoise comprising a half wave length horizontal conductor such as a copper tub e is connected at its midpoint to the exciter and reflector of a directional receiving antenna system by means of a short common down lead containing an adjustable impedance, the impedance between the reflector and the counterpoise being relatively large as compared to the exciter-counterpoise impedance. The counterpoise is horizontally positioned relatively close to the exciter and in a plane perpendicular to the direction of the incoming interfering waves. Undesired counterpoise currents are thus minimized or balanced and, as any change in the value of the impedance in the down lead affects the phase of the two currents a different relative degree, substantially any desired phase difierence between the two currents may be obtained.

The nature of this invention will be more fully understood from the following description taken in connection with the drawing, in which:

Fig. 1 represents an antenna-counterpoise system in which the balanced counterpoise is employed;

Fig. 2 represents an antenna system in which a plurality of antenna units are connected to ground through a common phase-varying impedance; and,

Fig. 3 shows a directional antenna system and associated transmission system in which both the balanced counterpoise and the counterpoise impedance are employed.

In Fig. 1 reference numeral 1 designates a portion of a zig-zag antenna, assumed to extend indefinitely in either direction from the portion disclosed and to regularly repeat the conformation so disclosed. The invention is not specific to the use of this type of antenna which was selectedas merely typical of present day transmitting or receiving antennae. Numeral 2 designates a counterpoise conductor. The counterpoise conductor is connected at its midpoint 3 to the antenna by means of down lead 4. Reference numeral5 represents a transformer having one winding 6 inserted in series with the down lead 4 and the other winding '7 connected to a translation system not shown on the drawing. 1he translation system may be either a transmitter or a receiver. Condensers 8 and 9, shown dotted, represent the capacities between any infinitesimal segment, such as segment 10, of the antenna 1 and the left and right hand section respectively of the counterpoise 2. There are, of course, corresponding capacities for the remaining segments of the antenna and in consequence thereof the capacities between the antenna, taken as 'in the first mentioned circuit.

a whole, and both counterpoise sections are in a sense symmetrical and balance each other.

The directions of the incoming desired and undesired waves are shown respectively by arrows 11 and 12. These directions shown are representative only and, as a matter of practice, the direction of the undesired wave varies in a plane perpendicular to the surface of the earth. The angle of propagation of the Waves, that is, the angle between the direction of propagation and the earth is, however, between 0 and degrees.

When employed in connection with a receiving system waves coming from the cooperating transmitting station, that is, waves having a direction 11, and waves coming from the opposite direction, as shown by arrow 12, induce electromotive forces along the counterpoise conductor 2. Ordinarily the most annoying waves are those which, in addition to having an undesired direction, as, for example, direction 12, have a wave length equal substantially to the operating wave length of the antenna. Considering waves coming from undesired direction 12 the electromotive forces induced along conductor 2 by the horizontally polarized component are similar in direction in both legs of the counterpoise and, in view of the fact that the counterpoise is perpendicularly positioned with respect to these undesired waves the infinitesimal voltages induced are in phase. Assuming that the resulting current present in the circuit comprising left hand section of counterpoise 2, winding 6, antenna 1, segment 10, and condenser 3 possesses the direction indicated by .the dotted arrows 13, the current in the circuit comprising right hand section of counterpoise 2, condenser 9, segment 10, antenna 1, and winding 6 will have the direction indicated by arrows 14; and this latter current will be opposite in direction in transformer winding 6 to the current These currents will therefore substantially tend to balance each other in the transformer winding inasmuch as they are in phase and opposite in direction. It should be noted here that a balance would also be obtained if the transformer were associated with the antenna in the manner shown in Fig. 2, that is, if it were included in the horizontal antenna member connecting the two vertical memn bers instead of in the down lead. Moreover, by m" positioning the counterpoise horizontally similar capacities, and hence similar impedances, are secured between the antenna and each side of the counterpoise so that substantial amplitude balance is also obtained. Consequently very =little, if any, undesired current flows through winding 6.

that the horizontally polarizedcomponent in a plane perpendicular to the direction of propaga- "tion of the undesired wave is principally responsible for inducing the undesired electromotive forces in the counterpoise. This is evident because the other polarized component which is ,perpendicular, in the above mentioned lane, to the horizontal component will not even if tilted, induce electromotive forces in horizontal conductors extending perpendicularly to the direction of propagation. This then constitutes a sec- 0nd reason for placing the counterpoise horizontal. That is, pick-up from the component perpendicular to the above mentioned horizontal component is minimized by utilizing a horizontal counterpoise. The verticaldown lead, however,

.does absorb some energy from this perpendicular component and it is therefore made as short as practicable. With respect to the horizontal com ponent an amplitude and phase balance of the undesired currents are affected, as pointed out above, regardless of the angle of propagation. Regardless of the theory, the optimum position of the counterpoise is horizontal since various experiments have shown that a minimum amount of undesired energy is present in the receiver proper when the counterpoise is horizontally positioned perpendicular to the plane of wave propagation.

Referring to Fig. 2, reference numerals 15 and 16 designate separate antennae or separate units of the same antenna system which are connected to each other through winding 17 of transformer 18, the other transformer winding 19 being associated with a translation system. Winding 17 is connected to ground 20 by means of down lead .21 having a sliding contact 22 at winding 17 and containing a phase-varying adjustable impedance 23. A suitable counterpoise may be employed in place of the ground, without affecting the result produced by the invention, since, in general, a counterpose is effectively a ground. In fact, the circuit may if preferred be designed to embody all the distinctive features of the system of Fig. 1.

Reference numeral 24 designates a relatively high impedance inserted between the antenna 16 and the winding 17. Condensers 25 and 26 shown dotted represent the impedance between ground 20 and antenna 15 and 16, respectively.

In operation, waves of the same or different phase are absorbed by antennae l5 and 16 and the resultant currents are conducted through impedance 23 to ground 20. Every substantial change in the value of impedance 23 affects the phase of both of these currents, but because of the large value of impedance 24 the current flowing in the circuit comprising antenna 15, contact 22, impedance 23, ground 20 and impedance 25 is affected to a much greater degree than that flowing in the circuit comprising antenna 16, high impedance 24, contact 22, impedance 23, ground 20 and impedance 26. Consequently, any desired difference in phase relation between the two antennae currents may be easily secured by varying impedance 23. A much finer phase adjustment may beobtained by moving contact 22 along windingl'7.

Specifically impedance 23 is here represented as an inductance and its function is to variably retard the phase of the current flowing from antenna 1-5'to ground 20 a much greater amount, relatively, than that flowing from antennalG to 1 I ground 20. Other phase varying means, such Supplementing the above explanation it is clear as a condenser, may be substituted, of course, for inductance 23 in which case the current from antenna 15 would be advanced a greater amount relative to that of the current from antenna 16.

Impedance 24 may in general be any suitable high impedance. For example, an impedance transformer, such as that described in a copending application of E. J. Sterba, Serial No. 282,--

210, filed September 16, 1930, and assigned to the applicants assignee may be satisfactorily employed, especially in short wave systems. The impedance transformer comprises a line an odd multiple of a quarter wave length long. By inserting a conductor one quarter wave length long i. 1

between winding l'7and antenna 16, in'the system shown in this figure a suitable impedance transformer is formed since the ground is in effectthe other conductor of the line. The surge impedance of the line is'high so'that the relatively small impedance between the antenna 16 and the ground 20 at the antenna is transformed to a very high impedance at winding 17 looking toward antenna 16. This may be written mathematically zs =zazw. where ZS equals the surge impedance of the line, Za the impedance at the antenna and Zw the impedance at the winding.

In Fig. 3, reference numerals 2'7 and 28 designate respectively, an exciter and a reflector of a directional antenna system, such as is disclosed in copending applications Serial Nos. 235,464 and 282,382, filed November 25, 1927 and June 2, 1928, respectively, all interest in which has been assigned to the applicants assignee. The exciter and reflector are placed a quarter wave length apart and are connected by means of a conductor 29 and a tuned circuit comprising adjustable condenser 30 and primary Winding 31 of transformer 32. This tuned circuit is located relatively close to the exciter so that the transmission conductor 29 connecting reflector 28 to the tuned circuit is approximately a quarter wave length long, whereas the length of the conductor from antenna 2'7 to the said circuit is so small that it may be disregarded. Primary winding 31 is connected to the midpoint 33 of a balanced counterpoise 34 by means of a down lead 35. This down lead is adjustably associated with the primary winding 29 by means of slidable contact 36. Reference numeral 3'7 designates a variable condenser inserted in the down lead for phase varying purposes.

The counterpoise 34 is a half wave length long and horizontally positioned preferably in the same vertical plane as the exciter. It extends in a direction perpendicular to the direction of the undesired incoming waves as represented by arrow 38 which is a significant fact with respect to the invention. It also extends, incidentally, perpendicular to the direction of the desired waves, which are incident from the opposite direction as indicated by arrow 39. p

The antenna system is inductively associated with the receiver by means of secondary winding 40 of transformer 32 which, with adjustable condenser 41, forms a tuned circuit. Numerals 42 and 43 designate the conductors of the line connecting the tuned circuit and the receiver proper and numeral 44 designates a sinusoidal transmission line comprising an outer tubular conductor and an inner conductor supported concentrically within saidouter conductor and insulated therefrom. This outer conductor is horizontally supported by brackets 45 approx mately one half foot above the ground, and the inner and outer conductors are conductively associated, respectively, with conductors 42 and 43. The outer conductor is grounded. The snake-like design of the line minimizes the straight line expansion of the conductors resulting from atmospheric temperature variations.

In operation, the electromotive forces induced in the exciter and reflector by incoming waves, having the direction shown by arrow 39, are substantially 90 out of phase. This phase relation is necessary in order to insure, in cooperation with the phase retardation effected by conductor 29, a cumulative eifect of direct and reflected waves at a receiver connected to secondary winding 40 through transmission line 44, or analogously, at a transmitter. They are not exactly 90 out of phase because, for one reason, the exciter acts as a screen. The desirable quarter cycle phase difference is obtained by the conductor 29 and also by adjusting condenser 37 and then, if

necessary, also slidably adjusting contact 36 along primary-winding 31. As in the system shown in Fig. 2, the desired phase difference is easily secured in this system since the reflector impedance is considerably higher than that of the exciter. In other words, the quarter wave length conductor 29 connecting the primary winding 31 and the reflector 28 transforms the reflector-to-counterpoise impedance to a maximum value as measured at the primary winding; and any change in capacity of the phase varying condenser 3'7 affects the phase of the exciter and reflector currents an unequal amount, relatively. Consequently, by properly setting the condenser 37 and adjusting contact 36 an exact quarter cycle out of phase relation is obtained.

Undesired voltages induced in the counterpoise by undesired waves, especially those from direction 33 are effectively balanced in the winding 31 in a manner similar to that described in connection with Fig. l, by placing the counterpoise 34 in a horizontal plane perpendicular to the direction of the undesired waves and symmetrical to both the exciter and reflector. This may be seen from the fact that the capacities between each side of the counterpoise and the exciter or reflector are similar; and that the undesired current flowing between one side of the counterpoise and a segment of the exciter or reflector opposes that flowing between the other side of the counterpoise and the same segment. Still further, and as again illustrated in Fig. 1, the geometry of the system, especially as affects the counterpoise, is such as to minimize the pick-up of waves by the counterpoise and therefore to reduce greatly the load on the balancing circuits immediately above described. The half wave length counterpoise also serves as a double openended quarter wave counterpoise and consequently oifers a minimum impedance for the received 115 current. In other words, two parallel paths, each of minimum impedance, are provided for the exciter and reflector currents, so that a maximum desired signal current is obtained.

The sinusoidal transmission system possesses 120 several distinct advantages over the ordinary transmission line. For example, a minimum amount of interfering energy is absorbed and only a relatively small amount of transmitted energy is reradiated in view of the facts that the line is comparatively close to the ground and also, in View of the fact that the line conductors are relatively close to each other. Furthermore, as stated before, the sinusoidal design minimizes the effects produced by temperature and atmospheric changes.

Although the invention has been described in connection with certain specific embodiments, it is to be understood that the various features described are not to be limited to these embodiments. In this respect it is obvious that any type of antenna employed in long or short wave systems, directional or otherwise, which differ in construction from those described, as, for example, open and looped antennae, may be successively employed in connection with the invention. It is equally clear that phase varying means, other than those shown or described, may be satisfactorily employed in place of the counterpoise impedance.

What is claimed is:

1. In combination, a directional antenna designed for a particular operating wave length, a counterpoise connected thereto and comprising a conductor, a half wave length long, or an odd 5!! multiple thereof, the counterpoise being positioned in a plane perpendicular to the known direction of an incoming undesired wave traversing said counterpoise and having a wave length equal, substantially, to the operating wave length.

2. In combination, a pluralityof antenna, cir cuits, the impedance of at least two of which are designed to be substantially different, and an adjustabl common impedance included in said last mention-ed circuits, said impedance having a small value compared to the remaining impedance of one of the last mentioned circuits and a large value compared to the remaining impedance of the other of said last mentioned circuits.

3. In combination, a plurality of antenna elements, a impedance and an inductance serially connected betwcen two of the said elements, and phase varying means having one terminal connected effectively to ground and the other terminal connected to said inductance.

l. In combination, a directional system comprising a plurality of antenna elements, a variable impedance having one terminal connected to at least two of the said elements and the other terminal connected to an effective ground, a conductor an odd multipl of a quarter Wave length long included between said impedance and one of the elements, and a translation system associated with said system.

5. In combination, a plurality of antenna elements, an inductance, a sliding contact associated with said inductance, said inductance being connected between two of the elements, and a conductor having one terminal connected to an efiective ground and the other terminal connected to said sliding contact, and a variable impedance in said conductor.

6. In combination, a directional antenna comprising an exciter and a reflector, an inductance, said exciter and reflector being connected to different points of said inductance, a variable imin circuit with the reflector and the counter-' poise.

' 8. In combination, a directional antenna comprising an eXciter and a reflector, a counterpoise conductor an odd multiple of a half wave length long, said counterpoise being horizontally positioned relatively close to said exciter in a plane perpendicular to the direction of undesired waves, an impedance having one terminal connected to the exciter and the other terminal to the reflector, phase varying means connected between said impedance and the mid-point of the counterpoise, and a relatively high impedance inserted between the reflector and the first mentioned impedance.

9. In a directional aerial system, an antenna comprising an exciter and a reflector, a transformer winding, an impedance transformer, said transformer winding and impedance transformer being serially connected and included between the exciter and the reflector, a counterpoise comprising one or more conductors at least one of which is an odd multiple of a half wave length long horizontally positioned in the vertical plane of the exciter and relatively close thereto, an adjustable condenser, a relatively short conductor connecting one terminal of the condenser tothe mid-point of the counterpoise conductor, and another relatively short conductor having one of its terminals connected to the other terminal of the condenser and its other terminal adjustably connected to the transformer winding, and a translation system inductively associated with said transformer winding.

HARALD T. FRIIS. 

